Troubleshooting 907 Engine & Gearbox Issues

Embarking on automotive maintenance can sometimes feel like navigating a labyrinth, especially when dealing with specific engine models like the Federal 907. This particular engine, known for its unique characteristics, can present a range of challenges for owners. Whether you're facing a stubborn gearbox that refuses to engage a particular gear, contemplating upgrades to your timing belt system, or looking to fine-tune your engine's performance through cam timing adjustments, understanding the intricacies of the 907 is key. This article aims to demystify some of these common issues, offering insights and potential solutions to help you keep your vehicle in top condition. We'll explore the nuances of gear selection, the benefits of different pulley and belt configurations, and the impact of cam timing on your engine's power delivery.

Investigating 5th Gear Engagement Problems

A common and frustrating issue reported by owners of vehicles equipped with the 907 engine is the inability to select 5th gear. This problem often manifests as the shifter feeling like it's hitting an obstruction, even after disconnecting the external shift linkage and attempting to engage the gear directly on the transaxle. Several factors could contribute to this:

Potential Causes for 5th Gear Inoperability:

• Relay Dog Misalignment: If the transaxle has been previously disassembled, a frequent culprit is the "Relay Dog" on the 5th gear selector shaft being out of its correct position. This is a relatively common oversight during reassembly, and the factory manual may not adequately detail the correct positioning. Fortunately, with the transaxle removed from the car, accessing and adjusting this component is straightforward, often only requiring the removal of the top cover.
• Reverse Lock-Out Feature: Another, albeit less likely if linkage is disconnected, possibility relates to the reverse lock-out mechanism at the base of the gear lever. A roll pin, situated on the front of the shift lever just above the pivot, interacts with a slot in a plate. If this roll pin is missing, bent, or if the lever mechanism allows excessive side-to-side movement, it can prevent the internal shift finger from aligning correctly with the notch on the 5th gear shift rail. This precise alignment is crucial for engaging 5th gear.
• Internal Gearbox Damage: While less common, it's also possible that there is internal damage to the 5th gear synchroniser or the gear itself. If the simpler adjustments don't resolve the issue, a more in-depth inspection of the gearbox internals may be necessary. This could involve removing the rear cover to expose 5th gear and its associated components.

It's important to systematically rule out the simpler explanations before assuming major internal damage. The advice given suggests focusing on the relay dog and the reverse lock-out pin first, as these are often easier to rectify without a full gearbox strip-down.

Understanding Timing Belt Pulleys: HTD vs. Non-HTD

When considering upgrades or replacements for your 907's timing drive system, the distinction between High Torque Drive (HTD) and non-HTD pulleys and belts is significant. The choice impacts reliability and the risk of timing belt slippage.

Trapezoidal (Non-HTD) Pulleys and Belts:

• These are the original, trapezoidal tooth designs.
• The teeth are shallower and do not engage as deeply with the belt.
• While functional, they are more susceptible to skipping a tooth if not maintained correctly or if subjected to excessive load.

HTD Pulleys and Belts:

• HTD systems feature taller teeth that engage much more deeply with the belt.
• This deeper engagement provides a more secure mesh, significantly reducing the likelihood of the belt jumping timing.

Advantages of HTD Conversion:

While the initial cost of converting to HTD pulleys can be substantial, the long-term benefits often outweigh the investment. The primary advantage is enhanced reliability. A slipped timing belt on an interference engine, such as many variants of the 907, can lead to catastrophic engine damage, including bent valves and piston damage. The increased security offered by HTD belts makes this failure mode far less probable, potentially saving you significant expense in engine rebuilds down the line.

Pulley and Belt Combination Recommendations:

If you are installing new pulleys, particularly if you are opting for adjustable pulleys to fine-tune cam timing (discussed later), the recommendation is to either purchase factory-specified 110 MOP HTD pulleys or use adjustable pulleys that can be precisely set to the 110 MOP timing. The latter requires a good understanding of engine mechanics, as incorrect installation on an interference engine can be costly.

Optimising 907 Engine Performance with Cam Timing

The camshaft timing plays a crucial role in an engine's power delivery characteristics. The Federal 907, with its C-cams, offers flexibility in tuning through adjustments to the intake and exhaust cam timing, often referred to by their Maximum Opening Point (MOP) or timing dots.

Stock Cam Timing:

Stock 907 engines typically use "C-cams" which are designed to be timed to a "design-correct" 110 MOP (indicated by red timing dots on the pulleys). However, some model year Federal emissions-compliant engines have the intake cam retarded to 100 MOP (indicated by blue dots). If your engine features dual MOP pulleys (both red and blue dots), you can revert the intake cam to the 110 MOP for improved performance.

Adjusting Cam Timing for Performance:

• Standard: Setting both intake and exhaust cams to 110 MOP is the standard approach for balanced performance.
• Intake Advance (104 MOP): Advancing the intake cam to 104 MOP, while keeping the exhaust at 110 MOP, can boost top-end power. This comes at the cost of slightly reduced low-end torque. For drivers who frequently operate in higher RPM ranges, this modification might be desirable. However, given the 907's already modest low-end torque, many find it counterproductive to sacrifice any further.

Important Considerations for Cam Timing Adjustments:

• Holistic Approach: Simply changing cam timing in isolation might not yield the desired results. It's often recommended to complement cam timing adjustments with changes to ignition timing and carburetor tuning. This ensures that all aspects of engine operation are working in harmony.
• Compression Ratio: While not explicitly detailed for a simple adjustment, increasing the compression ratio is another avenue for performance gains, though it typically involves more involved engine work.
• Emissions Testing: Be aware that modifying cam timing can affect emissions. If your vehicle is subject to emissions testing, ensure that your adjustments do not cause it to fail the test. In many regions, older vehicles are exempt from regular emissions testing, but this is not universal.
• Interference Engine Risk: As mentioned, the 907 is often an interference engine. Incorrect cam timing, especially when using adjustable pulleys without proper knowledge, can lead to piston-to-valve contact, resulting in significant engine damage. Always ensure you understand the procedure or have assistance from someone experienced.

Summary Table: Cam Timing Adjustments

Frequently Asked Questions (FAQ)

Q1: My 907 won't shift into 5th gear. What's the most likely cause?
A1: The most common causes are a misaligned "Relay Dog" within the transaxle (if it's been apart) or an issue with the reverse lock-out mechanism at the gear lever. Less likely, but possible, is internal gearbox damage to the 5th gear or its synchroniser.

Q2: Is it worth converting to HTD timing belts and pulleys?
A2: Yes, generally it is. While the initial cost is higher, HTD systems offer significantly improved reliability by reducing the risk of timing belt slippage, which can be catastrophic on an interference engine like the 907.

Q3: Can I adjust my cam timing to get more power?
A3: Yes, by adjusting the intake cam to around 104 MOP (Maximum Opening Point) while keeping the exhaust at 110 MOP, you can gain top-end power at the expense of some low-end torque. This should be done in conjunction with ignition and fuel system tuning for best results.

Q4: What are MOP and timing dots?
A4: MOP stands for Maximum Opening Point, referring to the point in the crankshaft rotation when the camshaft lobe is at its peak lift. Timing dots (like red for 110 MOP and blue for 100 MOP) are markings on the camshaft pulleys used to set this timing accurately.

Q5: How do I get a 907 engine out of a car?
A5: Removing a 907 engine typically involves disconnecting all fluid lines (fuel, oil, coolant), electrical connections, exhaust system, and engine mounts. It's usually lifted out from the top using an engine hoist or crane after securing the vehicle on jack stands. The transmission may need to be separated from the engine or removed as a unit, depending on the vehicle's specific configuration.

By understanding these common issues and potential solutions, 907 engine owners can approach maintenance and performance tuning with greater confidence, ensuring their vehicles remain reliable and enjoyable to drive.